The application of labels to articles and products has been and continues to be an important step in providing product identification, specific product information and marketing advantages. Manufacturers of various products are continually seeking a more efficient and effective manner in which to apply labels to articles or items, such as cartons, containers or any other packages or products having a surface capable of securely receiving an adhesive label.
Numerous methods have been employed in the past to mark articles, such as color-coded ink sprays and manually applied stickers. The introduction of adhesive-backed pressure sensitive labels and hand-held, manually operated applicators has greatly facilitated the marking of articles in that the applicators provide a simple means for applying an adhesive-backed label to an article. Such hand-held label applicators are well known and used extensively in various industries, for example, for marking the price of articles to be sold. Their use, however, in manufacturing, assembling and distributing applications is limited because of the necessity for marking many items at a high rate of speed. In these applications, the articles to be labeled are transported along a conveyor past a number of stations, one of which often entails the application of a label to each article as it passes by or while the conveyor is stopped. Use of a hand-held label applicator in this type of high speed operation would be unacceptably slow, inefficient, labor intensive and therefore, impractical due to the time constraints associated with high volume production.
As a result, relatively high speed labeling machines have been developed to apply labels to articles advancing by a labeling station on, for example, a conveyor belt. The pressure-sensitive labels are commonly precut and carried on a continuous web of material often called backing material which is rolled into a roll for mounting on the labeling machine. The backing material is somewhat more flexible than the label itself. This allows the label to be separated from the backing material, or dispensed, simply by bending the backing material sharply away frown the label, which is usually done by drawing the backing over a fairly sharp stripping or peeling edge of a peeling bar or plate. The less flexible label then separates from the backing material and remains relatively straight for application to the article by some type of applicator. For example, U.S. Pat. No. 4,267,004 to Anderson discloses a labeling machine using a peeler bar to remove labels from a web for application to articles.
Most labeling machines operate to intermittently move the web from a supply roll over the dispenser, e.g. peeler bar, to a take-up drum which accumulates the web of backing material. The intermittent movement of the web through the machine permits each label to be controllably dispensed at the precise time during the labeling process. In order for each label to be effectively dispensed, the label must be moved into a precise stop position adjacent the dispenser or peeler bar. Therefore, the driving device pulling the web through the machine must be capable of accurately and predictably starting and stopping the movement of the web so as to precisely position each label in the stop position adjacent the dispenser each time the web stops moving.
In labeling machines incorporating printers upstream of the dispenser, precise indexing of the web and stop positioning of each label is also necessary to ensure the complete and successful printing of each label. Many of these printers are of the standard reciprocating type which are normally activated during each deactuation period of the web driving device when the web and labels are stationary regardless of the position of each label. Therefore, if the web is moved too far or too little along the feed path, the labels will eventually become misaligned with the printer head resulting in ineffective printing. Accordingly, it is critical to use a web driving device capable of accurately and predictably indexing or metering a precise length of the web through the machine. Anderson '004 discloses a common type of driving device in the form of a nip roller assembly positioned upstream of a take-up drum. The conventional nip roller assembly includes a powered driver roller driven by a intermittently operated motor, e.g. stepper motor, and a nip roller biased against the driver roller to create a "nip" or pressure area through which the web is passed. The nip roller frictionally engages the web permitting the driver roller to accurately control the movement of the web. A label sensor positioned along the feed path senses the label, the gaps between the labels or other indicia on the web or labels, and sends a signal to a controller for stopping the driver roller. However, in certain applications, the environment of the labeling machine renders the nip roller assembly ineffective in metering the web. For example, in many plants, such as bakery and snack food processing and distribution plants, dust, dirt and grease in the air accumulates on the web and nip/drive rollers causing a reduction in friction between the rollers. This reduction in friction often causes slipping of the web through the nip thus resulting in misalignment of each label with the dispenser and printing device thereby adversely effecting both dispensing and printing.
Another commonly used type of driving device is a constant speed direct drive motor for driving the take-up drum, commonly referred to as a drive drum. The drive drum is intermittently rotated to move each label into a label stop position while accumulating the spent backing material on the drum. Deactuation of the drive drum occurs in response to a label stop position sensor signal indicating the next label to be dispensed is in position. Ideally, during each actuation period of the drive drum, the web moves a controlled, predictable distance so as to ensure each label is stopped in the correct label stop position adjacent the dispenser and while a different label upstream is precisely positioned in a label stop position adjacent the printer. However, an inherent time delay exists between the time at which the sensor senses the label or web and the moment at which the drive drum actually stops. During this time delay, the web continues to travel through the machine. Moreover, as the web of backing material accumulates on the constant speed drive drum, the diameter of the drum and accumulated web increases causing an increase in the linear velocity of the web through the machine. As a result, for a given roll of labels, the length of web indexed or pulled across the dispenser and printer during each the time delay associated with each actuation period of the drive drum increases thus undesirably varying the each label stop position relative to the dispenser and the printer causing ineffective dispensing and printing of labels.
U.S. Pat. No. 5,306,382 to Pichtel et al. discloses a labeling machine using a controlled speed take-up motor for driving the take-up drum. The motor speed is controlled so that the motor's angular velocity and torque are dependent upon the diameter of the web roll on the take-up drum in order to provide an essentially constant linear velocity thereby improving label registration. U.S. Pat. Nos. 3,934,837, 4,166,590 and 5,032,211 discloses other winding machines using variable speed winding mechanisms or motors to maintain constant web speed regardless of the increase in diameter of the take-up roll. However, variable speed motor assemblies are expensive relative to the low cost of constant speed motors. Moreover, it can be difficult to precisely control the speed of variable speed motors in response to an increase in take-up drum diameter so as to effectively maintain the correct label stop position.